QMediaPlayer: setPosition jumps to key frames

I want to jump to arbitrary position in a video (while the video don't play). When using a compressed format (H264), setPosition() jumps to the closest key frame (it seems to). How can I do to access images between key frames?
Here is the code
@
fMediaPlayer.play ();
fMediaPlayer.setPosition( pos );
fMediaPlayer.pause ();
@

fMediaPlayer is a QMediaPlayer. Note that it works when the video is compressed as jpeg.
Any idea of what's wrong ?

Thanks for the link. I'll give it a try.
I'm using video in a musical context. Arbitrary jump to any time location must be supported (while playing or not) and with accurate time synchronization with other medias. This is why I need setPosition().